Fermat's Room (12A)

There's something dreadfully pedantic about this locked-room mystery, though it occupies its 88-minute span quite neatly.

Four "genius" mathematicians are invited to spend a mystery weekend together in a remote house, their mission to solve a puzzle. But once inside the library of their unknown host the puzzle turns out to be a death-trap. The tension drains away quicker than you can say "Pythagoras".